Oparin and Haldane hypothesis



Chemical and physical processes combine to make primitive cells

  1. abiotic synthesis of small organic molecules (amino acids)
  2. small molecules join together (proteins)
  3. molecules packaged into primitive cells
  4. origin of self-replicating molecules


  • Early earth had water vapor and simple compounds from volcanic eruptions (CO2, CH4, NH3)
    • atmosphere was reducing (now controversial)
    • energy from UV or lightning
    • oceans = primordial soup of organic molecules

Miller & Urey experiments: Testing Oparin & Haldane


Similar experiments have had variable success


Fossils record is incomplete and biased


Fossils do trace the steps of animal evolution


Progression of life on earth



  • Fossils help divide geologic record into 4 eons
  1. Hadean
  2. Archaen
  3. Proterozoic


4. Phanerozoic: last 500 million years


  • Recent geologic ages (3), each with unique animal life
  1. Paleozoic
  2. Mesozoic
  3. Cenozoic

Review: Evolution of Eukaryotes and the Great Oxygenation


Early animal life and the Cambrian explosion




  • 2nd oxygen revolution tied to evolution of animals


  • Prior to Cambrian all large animals had soft bodies
    • little evidence of predation
    • grazers, scavengers, filter feeders
    • still all marine


  • Large predators evolve in early Cambrian
    • 545-525 mya
    • predator vs prey evolution
    • evolution of eyes

Cambrian explosion = bizarre aquatic creatures



  • Spectacular diversification of animals


  • Abrupt period: only 10-20 million years!
    • troubled Darwin


  • Hard skeletons and soft bodies
    • diverse body morphology (new Hox genes?)


  • Bilaterally symmetrical animals
    • formation of ‘head’ region
    • organized sensory organs
    • new direction of movement

Burgess Shale



  • British Columbia’s Yoho National Park
    • 60,000 unique fossils
    • one of the most diverse and well-preserved fossil sites


  • Creatures from the Cambrian explosion
    • origins dating 545 to 525 million years ago


  • Mudslides from land buried marine organisms
    • sediment deposited in deep-water basin next to enormous reef
    • soft and hard body fossils

Nearly all major animal groups in Burgess Shale!!!


Geologic history of plants and animals on land


First animal colonization of land



  • Arthropods (insects/spiders): 450 mya


  • Tetrapods (four-footed animals): 350 mya
    • evolved from lobe-finned fishes

Rise and fall of animal diversity



  • Diversification is not a smooth process


  • Speciation rates: how many species in a lineage are created


  • Extinction rates: how many species in a lineage are lost


  • The fate of a lineage depends on this rise and fall
    • plate tectonics
    • mass extinctions
    • adaptive radiations


  • Example: first tetrapods → dinosaurs → mammals

Continental Drift



  • Continents = floating plates of Earth’s crust
    • plate movement = continental drift
    • a few cm a year


  • Landmasses came together 3x over the previous billion years
    • yields new continents
    • new super continent in ~250 million years


  • Mountains and islands form at boundaries
    • India + Eurasia = Himalayan Mtns (45 mya)
    • Appalachian Mtns ~500 mya

Continental Drift…. so what?




  • Landmass change alters livable habitats
    • species distributions change
    • oceans change (Valley of Whales)
    • Pangaea (250 mya) drained shallow oceans


  • Landmass change alters climate
    • Canada was once tropical


  • Continental drift drives speciation
    • adapt, move or die

Allopatric speciation: Australian marsupials


Continental drift caused the success and failure of different mammal groups

Mass Extinctions


  • 5 mass extinctions in fossil record
    • ~75% of species go extinct


  • Permian extinction: 96% marine loss
    • most recent: Cretaceous (bye bye Dino)


  • Causes are varied
    • volcanoes & meteors
    • massive climate change
    • ocean chemistry


  • Evolution favors innovation but…
    • innovations can be wiped out

Adaptive Radiation


  • Rapid diversification events to fill new habitats


  • Occur on large scale after extinction events
    • many vacant habitats
    • favors evolutionary innovations


  • Can also occur when species reaches new open habitat
    • Opportunity leads to diversification


  • Dinosaur extinction → mammals
    • small & nocturnal in presence of dinosaurs

Regional Adaptive Radiation: Hawaiian islands born ‘naked’